[Issue Fixed]-Ubuntu20.04执行apt-get update报错:404 Not Found [IP: 91.189.91.38 80]

test@test:~$  sudo apt-get update
Ign:1 http://cn.archive.ubuntu.com/ubuntu groovy InRelease
Ign:2 http://security.ubuntu.com/ubuntu groovy-security InRelease
Ign:3 http://cn.archive.ubuntu.com/ubuntu groovy-updates InRelease
Err:4 http://security.ubuntu.com/ubuntu groovy-security Release
  404  Not Found [IP: 91.189.91.38 80]
Ign:5 http://cn.archive.ubuntu.com/ubuntu groovy-backports InRelease
Err:6 http://cn.archive.ubuntu.com/ubuntu groovy Release
  404  Not Found [IP: 91.189.91.38 80]
Err:7 http://cn.archive.ubuntu.com/ubuntu groovy-updates Release
  404  Not Found [IP: 91.189.91.38 80]
Err:8 http://cn.archive.ubuntu.com/ubuntu groovy-backports Release
  404  Not Found [IP: 91.189.91.38 80]
Reading package lists... Done
E: The repository 'http://security.ubuntu.com/ubuntu groovy-security Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://cn.archive.ubuntu.com/ubuntu groovy Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://cn.archive.ubuntu.com/ubuntu groovy-updates Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://cn.archive.ubuntu.com/ubuntu groovy-backports Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

解决方案:
sudo mv /etc/apt/sources.list /etc/apt/sources.list_backup
sudo vim /etc/apt/sources.list
然后填入下面信息，保存关闭即可:

deb http://old-releases.ubuntu.com/ubuntu/ groovy main restricted
deb http://old-releases.ubuntu.com/ubuntu/ groovy multiverse universe
deb http://old-releases.ubuntu.com/ubuntu/ groovy-updates main restricted
deb http://old-releases.ubuntu.com/ubuntu/ groovy-updates multiverse universe
deb http://old-releases.ubuntu.com/ubuntu/ groovy-backports main restricted
deb http://old-releases.ubuntu.com/ubuntu/ groovy-backports multiverse universe
deb http://old-releases.ubuntu.com/ubuntu/ groovy-security main restricted
deb http://old-releases.ubuntu.com/ubuntu/ groovy-security multiverse universe

参考:
Release not found in Ubuntu 20.10 (groovy) with ‘apt update’ [closed]
sources.list__20.10-groovy.txt